Conventionally, quick separation of a serum or a plasma from a blood is strongly required in blood testing etc. Generally, there are widely used methods of using the difference in specific gravity between blood corpuscle components (specific gravity approximately 1.08), and a serum or a plasma (specific gravity approximately 1.03) in separation of the serum or the plasma from the blood. Then, in separation of the serum or the plasma using the difference in specific gravity, various compositions, having a specific gravity adjusted in a range of 1.03 to 1.08, more preferably in a range of 1.04 to 1.06, for separation of the serum or the plasma have been proposed for quicker and more reliable separation of the serum or the plasma, etc. from the blood corpuscle component.
As such compositions for separation of a serum or a plasma, following patent document 1 discloses a composition for separation based on the difference in the specific gravity including a hydrogenated cyclopentadiene petroleum resin as a cyclic hydrocarbon oligomer, and a phthalic acid ester that is an aromatic esterified compound. The patent document 1 describes that the composition enables detailed setting of a specific gravity value, has outstanding separative power as a separating medium utilizing the difference in the specific gravity, and further avoids deterioration by chemical change or moisture absorption.
However, the composition for separation by the difference in the specific gravity described in the patent document 1 has poor compatibility between the components constituting the composition, leading to frequent separation of oily components. Accordingly, the oily components separated are liable to float in the serum or the plasma after centrifugal separation. That is, the above-described oily components that float as impurities in the serum or the plasma might cause clogging of a sampling nozzle of an analysis apparatus, and trouble in blood testing by attaching to the surface of an electrolyte sensor.    Patent document 1: JP, 9-15238, A